The present invention relates generally to the field of thin film inductors (see definition of “thin film inductor,” below) and more particularly to thin film inductors with laminated pole pieces (or “yoke pieces”) that are in the form of a stack of relatively thin layers alternating between magnetic material layers and insulating material layers.
The integration of inductive power converters onto silicon is one path to reducing the cost, weight, and size of electronic devices. One main challenge to developing a fully integrated power converter is the development of high quality thin film inductors. Thin film inductors for power conversion applications should store a large amount of energy per unit area to fit in the limited space on silicon. To accomplish this, ferromagnetic materials are used to increase the energy stored for a given current. However, ferromagnetic materials also introduce some disadvantages. Magnetic materials operating at high frequency produce losses through eddy currents and hysteresis. The eddy currents are created when the time varying magnetic fields in the yokes create an electric field that drives a circular current flow. These losses can be substantial and increase with the thickness of the yoke, and driving frequency of the inductor. Hysteresis losses can be created by magnetic domain walls in the yoke material. To enable efficient power conversion it is therefore critical to reduce the eddy current and hysteresis losses in the yokes.